The present invention relates to an implantable device with a specific surface roughness that facilitates in vitro formation of a solution mediated coating, including calcium phosphate coatings, in which biologically active substances can be coprecipitated. The present invention further relates to a process of producing such a device and to the biomedical use of such a device.
U.S. Pat. No. 5,456,723 discloses an implant having a porous metallic surface which has been treated by sandblasting and reductive acid etching resulting in a surface micro-roughness having a maximum peak-to-valley height of about 20 to 30 .mu.m and a roughness spacing of from 0.5 to 10 .mu.m, preferably of about 1-5 .mu.m. The extremely sharp, comb-like structure is necessary in order to achieve sufficient adhesion between the implant and the coating material (hydroxyapatite) formed on it by anchoring the hydroxyapatite in the implant.
A drawback of most hydroxyapatite-coated implants is that the anchoring of hydroxyapatite onto the implant requires high processing temperatures, which limit the choice of substrate materials and result in higher processing costs. The previously preferred technique for coating implant materials with hydroxyapatite is plasma deposition (for a review, see P. Serekian, in Hydroxylapatite Coatings in Orthopaedic Surgery, Ed. Geesink and Manley, Raven Press N.Y., 1993, p. 81-87). Another disadvantage of the plasma deposition technique, in addition to the high temperatures involved, resides in the relatively large particle size, in the order of 30-70 .mu.m.
An aim of the present invention is to provide a coated implantable device that can be used in a wide variety of biomedical applications (surgery, bone-replacement, prosthodontics etc.). The device should give rise to effective bone formation and simultaneously result in a desired biological effect, such as assisting bone formation, preventing infection or rejection during or after implantation, induced by the presence of biologically active substances, such as proteins, growth-factors, lipids, (lipo)polysaccharides, cytostatic agents, hormones, antibiotics or other biological agents. In case a degradable coating is produced, degradation of said coating due to solution mediated processes or cell mediated processes should result in a further exposure or release of biologically active agents. The processing of the device and the temperature at which it is produced should not have an adverse effect on the biological activity of said agents.